Apparatus and method for debugging electronic components through an ICE

ABSTRACT

A circuit controlling the transmission of information from a testing probe to an ICE™ base unit for debugging an electronic component having a dedicated bus. The circuit comprises a plurality of gate arrays coupled together to operate in a pipeline fashion. Each of the plurality of gate arrays includes a bus tracking component, a formatting component, filtering circuitry and address translation circuitry. The bus tracking component monitors the dedicated bus and transfers internal command signals to its associated formatting component and formatting components of the other gate arrays. The formatting component transfers only completed data to the ICE™ base unit for tracing. If in &#34;Format&#34; mode, the formatting component synchronously aligns the completed data and its associated addressing information before transferring such information to the ICE™ base unit. In &#34;Raw&#34; mode, however, information from the electronic component is immediately transferred to the ICE™ base unit without alignment. The filtering circuitry enables selective tracing of a type(s) of bus cycle(s) by signaling the ICE™ base unit whether or not to trace the frame during this particular bus cycle. The address translation circuitry calculates various address information required by the ICE™ base unit but is not transmitted by the electronic component to minimize required operations by word recognizers in the ICE™ base unit.

CROSS-REFERENCES TO RELATED APPLICATIONS

This is a §1.60 Continuation application of application No. 08/575,252, filed Dec. 20, 1995, which has matured into U.S. Pat. No. 5,537,536, issued Jul. 16, 1996, which is a §1.62 Continuation application of application No. 08/263,134, filed Jun. 21, 1994, now abandoned.

BACKGROUND OF THE INVENTION

1. The Field of the Invention

The present invention relates to the field of integrated circuits. More particularly, the present invention relates to an apparatus and method for debugging an electronic component or software executed by the electronic component to correct logical errors or programming errors, respectively.

2. Background of Art Related to the Invention

For many years, integrated circuit designers and software programmers have used an in-circuit emulator ("ICE™") to debug software code or hardware, typically a central processing unit ("CPU") defined herein as an "intelligent" integrated circuit such as a microprocessor, micro-controller and the like. The ICE™ is a non-intrusive debugging tool that uses external hardware to emulate operations of the CPU embedded in a target system (i.e., a product prototype). As a result, certain results (output voltages, contents of storage elements, etc.) from these operations are traced (i.e., recorded) in memory of the ICE™.

The external hardware consists of a conventional testing probe which latches information from the CPU and directly uploads the information to an ICE™ base unit for storage in trace memory and later retrieval therefrom for debugging purposes. The conventional testing probe includes a number of programmable CMOS logic cell arrays ("LCAs") such as, for example, XC 2000 or 3000 series manufactured by Xilinx, Inc. of San Jose, Calif., which are electrically connected with the CPU mounted on the conventional testing probe. The CPU is then electrically connecting the target system as if it was embedded in the target system. The LCAs are arranged into a circuit for latching information from the CPU and transferring such information to the ICE™ base unit through a communication link. However, this construction affords many disadvantages.

One disadvantage associated with the conventional testing probe is that it merely transfers information between the CPU and the ICE™ base unit without being able to modifying the information in certain situations to reduce communication complexity between the LCAs and the ICE™ base unit as well as the LCAs themselves.

Another disadvantage associated with the conventional testing probe is that the LCAs typically can not support CPUs operating at high frequencies in the range of 65 mega-hertz ("MHz"). Thus, with advancements in CPU technology, these conventional testing probes will prohibit the ICE™ from debugging these CPUs and perhaps such software controlling the CPUs.

A further disadvantage is that LCAs within the conventional testing probe are incapable of performing a number of desired functions, including but not limited to filtering bus cycles for selectively tracing a particular type(s) of bus cycle(s), eliminating storage of unnecessary information in the ICE™ base unit (typically due to wait states and/or termination of the current bus cycle) and tracing snoop bus cycles to ascertain all activity on the CPU bus.

Yet another disadvantage associated with the conventional testing probe is that it is incapable of outputting information, particularly data and address, to the ICE™ base unit in a synchronous manner to increase performance efficiency by as much as fifty percent (50%).

Another disadvantage is that the conventional testing probe is incapable of generating address information required by the ICE™ base unit in the event that such address information is not provided by the CPU.

Therefore, it is contemplated that there exists a need for a circuit within the testing probe for enabling a CPU or software to be debugged at high operating frequencies (≧65 MHz), reducing complexity of the ICE™ base unit and enabling many additional functions to be performed. Therefore, it is an object of the present invention to employ a circuit for assisting the ICE™ system for debugging purposes.

It is an object of the present invention to provide a circuit which reduces the complexity of the ICE™ system and thus, the complexity of the software controlling the ICE™ system.

It is another object of the present invention to provide a circuit for tracing the CPU bus during a DMA Operation by an external agent, provided the external agent abides by the specific protocol of the CPU.

Another object of the present invention is to allow software to begin at any location in the trace and start decoding bus cycles.

Yet another object of the present invention is to transmit packets of completed data to the ICE™ base unit for easy tracing of bus sequences, thereby avoiding errand data from being sent before completion of a desired bus cycle.

It is another object of the present invention to provide a circuit which increases the efficiency of the ICE™ base unit.

Another object of the present invention is to provide a circuit operating in conjunction with the ICE™ base unit to trace Snoop activities.

BRIEF SUMMARY OF THE INVENTION

In light of the foregoing, it is appreciated that there exists a need for a circuit and method controlling the transmission of information from a testing probe to an ICE™ base unit for debugging an electronic component operating at high frequencies. The present invention comprises a plurality of gate arrays coupled together to operate in a pipelined fashion. Each of the gate arrays includes a bus tracking component, a formatting component, filtering circuitry and address translation circuitry.

The bus tracking component of one of the gate arrays monitoring the CPU bus and transfers internal command signals to its formatting component as well as those formatting components with other gate arrays. These internal command signals provide control information to the formatting components of each of the gate arrays to indicate when to latch information and/or transfer the information to the ICE™ base unit. The bus tracking component comprises three state machines. A first state machine generates a first internal command signal "LEADS" indicating that a snoop cycle has occurred on the CPU bus. A second and third state machines operate in the alternative to track bus cycles on the CPU bus during non-DMA and DMA operations, respectively.

The formatting component transfers only completed data to the ICE™ base unit for tracking sequences. In Format mode, the formatting component synchronously aligns the completed data and its associated addressing information before transferring such information to the ICE™ base unit. In "Raw" mode, however, information from the CPU is immediately transferred to the ICE™ base unit without alignment. The formatting component comprises a holding element and a formatting controller. The holding element is a combinatorial logic circuit including storage elements for holding data or address, snoop request addresses and a write back replacement address and multiplexers for selecting when certain information is to be transferred. The formatting controller includes four state machines for controlling the operations of the holding elements in transferring information to an ICE™ interface circuit being a generic combinatorial logic circuit to select which information is transferred to the ICE™ base unit.

The filtering circuitry enables selective tracing of a type(s) of bus cycle(s) by signaling the ICE™ base unit whether or not to trace the frame input during this particular bus cycle. The filtering circuitry comprises a bus cycle filter and a force filter. The bus cycle filter generates either an active signal if the bus cycle is one of a selected bus cycles or an inactive signal. This signal is transmitted through an output filter line to the force filter. The force filter, on the other hand, is primarily used to filter non-bus type cycles. In the event that either the bus cycle filter or the force filter detects a selected bus or non-bus cycle, a valid trace frame signal is asserted to inform the ICE™ base unit to trace the frame.

The address translation circuitry calculates various address information required by the ICE™ base unit but is not transmitted by the CPU. Such address information includes (i) an upper boundary constraint AH[2:0] to provide the ICE™ base unit with the highest byte address currently on the CPU bus and (ii) a lower boundary constraint A[2:0], collectively with AH[2:0], to provide the ICE™ base unit with a range of byte addresses on the CPU bus. This range allows word recognizers in the ICE™ to recognize byte addresses on a byte granularity whereas without such range, the word recognizers would recognize byte addresses on a packet granularity. The address translation circuitry further alters certain byte enable and address values depending on certain events. More specifically, in the event that the CPU alters its current bus cycle from a non-burst read cycle to a burst read cycle, the outputs BE[3:0]# are set to "0". Otherwise, BE[3:0]# and AM[2:0] are set to "1". Furthermore, in the event that there exists a burst cycle, A[4:3] is incremented as needed to signal burst cycles. The manner of incrementing AH[2:0] is shown in the fifth combinatorial logic circuit of the ICE™ interface circuit.

BRIEF DESCRIPTION OF THE DRAWINGS

The objects, features and advantages of the present invention will become apparent from the following detailed description of the present invention in which:

FIG. 1 is a perspective view of an in-circuit emulation ("ICE™") system having a testing probe incorporating a plurality of gate arrays forming the present invention.

FIG. 2 is a circuit diagram of a preferred embodiment of the present invention incorporated within a plurality of gate arrays.

FIGS. 3A-3C is a more detailed circuit diagram of one of the plurality of gate array wherein the gate array comprises a bus tracking component, a formatting component, filtering circuitry and address translating circuitry.

FIG. 4 is a circuit diagram of the bus tracking component.

FIG. 5 is a circuit diagram of the holding element of the formatting component.

FIG. 6 is a circuit diagram of the formatting controller of the formatting component.

FIG. 7 is a timing diagram of trace signal outputs during normal operations by the CPU.

FIG. 8 is a circuit diagram of the ICE™ interface circuitry coupled to the formatting component.

FIG. 9 is a circuit diagram of the bus cycle filter of the filtering circuitry.

FIG. 10 is a circuit diagram of the force filter of the filtering circuitry.

FIG. 11 is a circuit diagram of a first portion address translation circuitry designed to calculate the high address boundary constraint "AH[2:0]".

FIG. 12 is a circuit diagram of a second portion of the address translation circuitry for calculating the three least significant bits of the address "A[2:0]".

DETAILED DESCRIPTION OF THE INVENTION

In the following detailed description, the present invention describes a circuit operating in association with a testing probe of an ICE™ designed for actively assisting an ICE™ base unit to debug (i) an electronic component, typically a CPU, operating in a "target" system and/or (ii) software controlling operations of the CPU. In the present application, numerous details are set forth, such as specific combinatorial logic circuits (i.e., an interconnection of standard logic gates, latches, and/or other components which produce at least one output control signal), specific circuit diagrams of gate arrays and components forming the gate arrays and the like. It is apparent, however, to one skilled in the art of circuit design, that the present invention may be practiced through different embodiments than illustrated without deviating from the spirit and scope of the present invention.

In the detailed description, a number of terms are frequently used to describe certain control circuits, signal representations and CPU bus operations which are defined herein. A "state machine" is a combination of conventional logic, typically synchronous in nature, which receives as input at least one control signal containing state information and responds to the control signal through at least one control output. A "multiplexer" is defined as one or more conventional multiplexing logic gates represented as having two inputs arranged to output one of two inputs. A "packet" is generally defined as a plurality of information bits (i.e., binary values of address, control or data signals) being a maximum 64-bits in width, which are transferred in a single bus cycle. The packet may be further categorized according to its contents e.g., a "data packet" being a packet of exclusively data. A "frame" is generally all of the information bits being output from the gate arrays of the testing probe in a single clock cycle.

Additionally, a "bus cycle" is an operation by the CPU which is commenced by driving an address onto the CPU bus and asserting an address strobe signal and is completed by asserting a signal such as a "bus ready" signal. The bus cycle may include a single data transfer or multiple data transfers (i.e., four sequential data transfers are collectively referred to as a "burst" cycle). A "bus sequence" is a series of bus cycles to perform a specific function.

Referring to FIG. 1, the ICE™ 1 comprises a testing probe 2 capable of retrieving information on a CPU bus 3a and transmitting re-formatted information to an ICE™ base unit 4 for storage, word recognizing and state sequencing. In a preferred embodiment, the CPU 3 is an Intel® Pentium™ CPU supporting a 64-bit data bus and a 32-bit address bus; however, it is contemplated that the testing probe 2 clearly could be modified in accordance with any CPU specification. For illustrated purposes, however, the description of the preferred embodiment will be discussed in the context of debugging the Pentium™ CPU, although such discussion should not be construed in any way as a limitation on the scope and spirit of the present invention.

One embodiment of the testing probe 2 includes a connector 5 for mechanically and electronically coupling the testing probe 2 to a target system 6 (e.g., a printed circuit board operating as a CPU system) and a plurality of gate arrays 10-14, being standard 0.8 μm CMOS Applied Specific Integrated Circuits, for monitoring information signals output from the CPU bus 3a. The CPU 3 is mounted onto the testing probe 2 after removal from the target system 6 in order to establish electrical contact with the gate arrays 10-14 while still maintaining its pre-removal electrical contact within the target system 6 through the connector 5. If the testing probe 2 is in an appropriate operation mode, it re-formats the information signals from the CPU bus 3a and transfers re-formatted information to the ICE™ base unit 4 through corresponding cables 7 (i.e., ribbon, flex, etc.). The ICE™ base unit 4 operates according to a specific protocol to ascertain whether it should commence "tracing" (i.e., storing) of the re-formatted information. If the ICE™ base unit 4 traces the re-formatted information and detects a command (usually transmitted by a computer system accessible by a test operator) from a state machine within the ICE™ base unit 4 to discontinue such tracing, the traced re-formatted information is uploaded to the computer system 8 through a communication link 9 for formatting and displaying the information in a visual format and storing the information in a retrievable format.

The testing probe 2 operates in one of three modes; namely, a "Raw" mode, "Format" mode and "Pseudo-Format" mode. In Raw mode, the testing probe 2 monitors information on the CPU bus and generates re-formatted control signals to the ICE™ base unit 4. Such control information is transferred in its entirety as received to the ICE™ base unit 4. This is accomplished by the gate arrays 10-14 emulating that a bus cycle is completed every CLK cycle (defined below). The main purpose of the Raw mode is usually for hardware debug of state machines and interconnects of the target system 6. In the Format mode, the testing probe 2 monitors information output on the CPU bus and generates re-formatted signals similar to "Raw" mode. However, the testing probe 2 synchronously aligns (i.e., simultaneously outputs) these re-formatted signals in order to transfer information to the ICE™ base unit 4 after its associated bus cycle has completed, thereby reducing the amount of signal analysis required by the ICE™ base unit 4. Finally, in the Pseudo-Format mode, the testing probe 2 operates alternatively in either the Raw or Format mode, depending on whether a hold acknowledge ("HLDA") signal input into the CPU 3 is asserted or de-asserted, respectively. This is normally done for software debugging of DMA sub-systems.

Referring to FIG. 2, although each of the plurality of gate arrays 10-14 may be identical in physical construction to reduce masking and other manufacturing costs, each gate array may be configured to function in a different manner by programming its respective configuration elements 15-19 (e.g., Configuration registers) differently. The configuration elements 15-19 are programmed to select various logic gates (usually multiplexers) within its gate array so that, if desired, each gate array may have a different signal path than the others. Each of the configuration elements 15-19 is accessed for programming purposes through its serial communication port 20a-20e. For example, in this preferred embodiment, a well-known five-pin Joint Test Action Group ("JTAG") serial port (IEEE standard 1149.1) is used to program the configuration elements 15-19.

Depending on how its configuration element 15-19 is programmed, a gate array propagates information through a particular signal path. In the preferred embodiment, the first gate array 10 is configured to receive and monitor a first data packet ("D[31:0]") input into a first port (labeled "TIN[31:0]") from the CPU bus; a plurality of internal command signals input into a second input port (labeled "TIC[7:0]") from the fifth gate array 14; and a plurality of byte enables "BE[3:0]#", being active-low as identified by a "#" symbol, input into a third port (labeled "TIC[11:8]") from the third gate array 12. Thereafter, the first gate array 10 transfers and possibly re-formats a first 36-bit packet to the ICE™ base unit from a first output port labeled "TOUT[31:0]/BEN[3:0]" as enumerated in Table 1 of Appendix A. The 32 least significant bits of the first packet (TOUT[31:0]) are data bits which are stored in trace memory of the ICE™ base unit 4. The four most significant bits (BEN[3:0]), however, are simply used by word recognizers (i.e., range comparators) and state machines in the ICE™ base unit and are not stored in the trace memory. The first gate array 10, as well as the other gate arrays 11-14, further transmits a clock signal ("TCLK") being a buffered version of a CLK signal (defined below) to be used by the ICE™ base unit to timely latch its packets.

The second gate array 11 operates in a manner identical to the first gate array 10, except that it is configured to receive and monitor a second data packet containing a most significant 32-bits of data ("D[63:32]") input into the TIN[31:0] from the CPU bus and a second plurality of byte enables ("BE[7:4]#") input into TIC[11:8] from the fifth gate array 14. The second gate array 11 further receives the plurality of internal command signals into its second input port. The second gate array 11 transfers and possibly re-formats a second 36-bit packet from TOUT[31:0]/BEN[3:0] (see Table 2 of Appendix B for its contents).

The third gate array 12 is configured to receive and monitor as input a third packet from the CPU bus including 21-bits of address starting at a fourth address bit ("A[23:3]") and a plurality of byte enables ("BE[7:0]#") into TIN[31:0] (see Table 3 of Appendix A) and the plurality of internal command signals from the fifth gate array 14. Based on these inputs, the third gate array 12 calculates the three least significant bits of the address ("A[2:0]") and a high address boundary constraint "AH[2:0]". Thereafter, the third gate array 12 transfers a third 36-bit packet to the ICE™ base unit. The third 36-bit packet includes the least significant 24 bits of the address "A[23:0]" and the plurality of byte enables BE[7:0]# (both of which are stored in trace memory) and the high address boundary constraint "AH[2:0]". The third gate array 12 further outputs the plurality of byte enables from a second output port "TOC[7:0]" through a byte-enable bus 21 (discussed below). The third gate array 12 generates A[2:0] and AH[2:0] since these signals are required by the ICE™ base unit to determine what address range is covered by the current address in the event of a burst cycle.

The fourth gate array 13 is configured to receive and monitor a fourth 32-bit packet input into TIN[31:0] from the CPU bus. The fourth packet includes the most significant bytes of the address "A[31:24]" and various snoop and control signals as listed in Table 4 of the Appendix A and defined in Appendix B. Moreover, the internal command signals are input into its second input port "TIC[7:0]" in order to assist in re-formatting the information output to the ICE™ base unit in the fourth 36-bit packet by indicating when to latch certain information and transfer such information to the ICE™ base unit.

The fifth gate array 14 is configured to receive and monitor a fifth packet including majority of the control signals input into its first input port "TIN[31:0]" from the CPU bus as listed in Table 5 of Appendix A and defined in Appendix B. The plurality of byte enables BE[7:0]# from the third gate array 12 are input into TIC[7:0] of the fifth gate array 14 through the byte-enable bus 21 for cycle type filtering. Based on these inputs, a number of re-formatted signals are transferred to the ICE™ base unit including a TCLK signal, a fifth 36-bit information packet which comprises a number of control signals including trace output signals providing trace and control information and the internal command signals which are output from the second output port. "TOC[7:0]" to each of the first-fourth gate arrays 10-13 (hereinafter referred to as the "remaining gate arrays") through an inter-communication bus 22.

As further shown in FIG. 2, the plurality of gate arrays 10-14 are clocked by any identical clock line 23 which transmits a common buffered clock ("CLK") signal to each gate array 10-14. The CLK signal is derived from an original clock signal of the CPU which is driven into a phased lock loop "PLL" to generate the CLK signal. As a result, the gate arrays 10-14 operate in a synchronous manner. The plurality of gate arrays 10-14 are further coupled together by the inter-communication bus 22 and the byte-enable bus 21 as shown.

As also shown in FIG. 2, the inter-communication bus 22 inputs the plurality of internal command signals generated by a fifth gate array 14 into each of the remaining gate arrays 10-13. These internal command signals provide control information from which a trace signal output can be derived for latching information and/or transfer the information to the ICE™ base unit (i.e., when to re-format the information signals and transfer such re-formatted information signals to the ICE™ base unit). The byte-enable bus 21 is primarily used to signal which bytes of data are to be written to external memory as required by the CPU for a current bus cycle. The byte-enable bus 21 is coupled in its entirety to the fifth gate array 14, but only half of the byte-enable bus 21 is coupled to the first gate array 10 while the other half of the byte-enable bus 21 is coupled to the second gate array 11. Thus, the first gate array 10 monitors a first half of the CPU bus and the second gate array 11 monitors a second half of the CPU bus where each byte-enable is used to specify whether its associated data byte is valid.

Referring to FIGS. 3A-3C, a preferred embodiment of a gate array 30 having a physical construction identical to each of the plurality of gate arrays is illustrated in a more-detailed circuit diagram. The gate array 30 comprises a bus tracking component 31, a formatting component 32, filtering circuitry 33a and 33b and address translating circuitry 34a-34c. These components and circuitry are coupled together through a variety of combinatorial logic circuits in order to monitor information signals from the CPU, re-format the information signals and transfer such re-formatted information signals to the ICE™ base unit.

These combinatorial logic circuits include latches such as conventional D-type flip-flops and other similar logic in order to ensure proper hold and set-up timing for synchronous operations between gate arrays and synchronous output of the re-formatted information signals to the ICE™ base unit. The latches have been illustrated but frequently are not discussed for clarity sake. These combinatorial logic circuits further include a plurality of multiplexers 45a-45e each having two inputs "A" and "B" as labeled. As briefly alluded to above, these multiplexers, selected by one of the configuration elements 15-19, enable the first-fifth gate arrays to enjoy different signal paths while maintaining the same physical construction. For clarity sake, a table indicating which inputs of the multiplexers 45a-45e are selected for each the gate array is illustrated below. The symbol ("X") means that either input may be selected.

                  TABLE A                                                          ______________________________________                                         Selected Multiplexer Inputs                                                    Gate Array                                                                     Multiplexer                                                                            FIRST    SECOND   THIRD  FOURTH FIFTH                                  ______________________________________                                         FIRST   B        B        A      B      B                                      SECOND  A        A        B      X      X                                      THIRD   X        X        A      X      B                                      FOURTH  B        B        B      B      A                                      FIFTH   A        A        A      A      B                                      ______________________________________                                    

The gate array 30 receives information through at least three input ports 35-37 and a serial communication port (e.g., JTAG) 38 and transmits information form a plurality of output ports 39 and 40. The first input port 35 of the gate array 30 ("TIN[31:0]") is a 32-input port for receiving a packet of information (i.e., data, address and/or control signals) from the CPU through a plurality of signal lines 41. Of course, these signal lines 41 are coupled to different outputs of the CPU, depending on the particular gate array.

The information signals of the packet are latched by a latch element 42 and thereafter, a majority of these information signals are input into the bus tracking component 31 and a first pipe component 43a. The first pipe component 43a includes multiple latches coupled together in series to provide sufficient latency between input and output. Additionally, certain information signals from TIN[31:0] are input into various other components since these different gate arrays are required to transfer different information signals and a common structure is used. More particularly, those signals associated with TIN[31:24] are input into a first and second portions 34a and 34b of the address translating circuitry labeled as "AT1" and "AT2" and a third multiplexer 45c to be output through the byte-enable bus 21. Moreover, the information signals of TIN[2:0] are input into a first multiplexer 45a and the information signal of TIN[3] is input into a second multiplexers 45b. In addition, the information signals TIN[17:16] are input into a fifth multiplexer 45e operating in connection with a force filter 33b of the filtering circuitry.

Referring to FIG. 4, the bus tracking component 31 includes three state machines 50-52 operating as a single unit to generate and transfer the internal command signals (defined below) for tracking the CPU bus and controlling the formatting component to transfer re-formatted information into the ICE™ base unit in a synchronous manner during "Format" mode. A first state machine 50 generates a first internal command signal, Latched External Address Strobe ("LEADS") which is used to indicate that a "Snoop" cycle has occurred on the CPU bus in order to instruct certain state machine(s) within the formatting component 32 of such occurrence. The LEADS signal is based on a number of control signals including HLDA, AHOLD, EADS#, HITM# and BOFF# which are defined in Appendix B. The LEADS signal is active when there is a valid snoop address, being asserted on the Pentium™ CPU, is output from the bus tracking component 31 via a first internal command line 53.

A second and third state machines 51 and 52 operate in the alternative to track bus cycles on the CPU bus. The selection of either the second or third state machines 51 or 52 is dependent on whether the HLDA signal is asserted indicating that a DMA operation is in progress. If the HLDA signal is asserted, the third state machine 52 is in operation while the second state machine 51 remains inactive. If the HLDA signal is de-asserted resetting the third state machine 52 and a Reset line 54 is inactive, the second state machine 51 becomes active; however, if the Reset line 54 is active, the second state machine 51 is reset and the third state machine 52 is active. If protocol errors occur in the second state machine 51, the ICE™ base unit freezes. If protocol errors occur in the third state machine 52, the third state machine 52 flushes all bus cycles and does not accept any new ones.

Each of the second and third state machines 51 and 52 receive as input those control signals inputted into the first input port ("TIN[31:0]") identified by "*" in Table 5 of Appendix A. These control signals are used to generate four additional internal command signals; namely, Valid Data ("VD"), Valid Address ("VA"), Valid Burst ("VB") and Abort ("ABORT"). These four internal command signals from each state machine 51 and 52 are OR'ed together through conventional logic gates 55 to represent when a DMA or non-DMA operation dictates assertion of these command signals. Although it is contemplated that the second and third state machines 51 and 52 are separate as a design choice, it is contemplated that the state machines could be combined so long as the combination functions properly.

The VD command signal indicates whether the CPU recognizes the data. The VA command signal indicates whether the CPU has initiated a bus cycle with a valid address and associated control signals. The VD and VA signals are output from the bus tracking component 31 through a second and third internal command lines 56 and 57. Another one of the plurality of internal command signals includes the VB command signal which indicates whether the CPU is transferring or receiving four 64-bit data packets in a burst cycle. The VB command signal is output from the bus tracking component 31 through a fourth internal command line 58. Another of the internal command signals includes the ABORT command signal which indicates that an external agent requires immediate termination of current bus cycle(s) through its assertion on a fifth internal command line 59. While operating in Raw mode, the third state machine 52 activates the VD and VA signals and de-activates VB and ABORT signals to emulate that the CPU is completing a bus cycle every CLK cycle. Thus, all of the control signals on the CPU bus are transferred to the ICE™ base unit and are traced by the ICE™ base unit.

Referring back to FIGS. 3A-3C, although the bus tracking component 31 is incorporated within each gate array for manufacturing cost savings, only the bus tracking component 31 for the fifth gate array is operational due to the pipeline nature of the gate arrays. Thus, the remaining gate arrays depend on the fifth gate array for these above-described internal command signals.

For illustrative purposes, assuming that the gate array 30 is the fifth gate array, the bus tracking component 31 transfers the internal command signals through two different signal paths. Along a first signal path, the bus tracking component 31 outputs the internal command signals to the remaining gate arrays by transmitting the internal command signals into the third multiplexer 45c, which is selected by its configuration element 19 to output the internal command signals through the second output port 40 labeled "TOC[7:0]". TOC[7:0] of the fifth gate array is coupled to the second input ports 36 "TIN[7:0]" of the remaining gate arrays through the inter-communication bus line 22 (see FIG. 2). The internal command signals are then input into a first input of the fourth multiplexer 45d of that gate array.

Concurrently, along a second signal path, the internal command signals are latched for two clock cycles before being input into a second input of the fourth multiplexer 45d of the fifth gate array. The reason for such delay is that there exists a delay of two clock cycle from generation of the internal command signals in the bus tracking component 31 of the fifth gate array 14 to such signals being input into the fourth multiplexer 45d of another gate array. Thus, the internal command signals are synchronized to be input into each fourth multiplexer 45d of the gate arrays simultaneously. The configuration element for the remaining gate arrays selects the first input of the fourth multiplexer 45d of the remaining gate arrays while the configuration element for the fifth gate array selects the second input so that the internal command signals are input into the formatting component 32.

The formatting component 32 comprising a holding element 60 and a formatting controller 110 for controlling the operation of the holding element 60. As shown in FIG. 5, in the preferred embodiment of the present invention, the holding element 60 is a combinatorial logic circuit comprises a plurality of "stages" 61-64 where each stage includes storage elements or multiplexers, all of which are operating in concert to provide temporary storage and proper latency and set-up timing. A first stage 61 of the holding element 60 includes at least four storage elements 65-68 (e.g. each storage element being a number of D-type flip flops with an enable input or any equivalent element) which are employed for temporarily storing information, mainly data and address from the CPU bus (hereinafter referred to as "information storage elements"). One of these information storage elements 65-68 is selected by activating its corresponding address/data ("A/D") enable line 69-72, respectively. Additionally, the first stage 61 includes at least four storage elements 73-76 for temporarily storing a snoop address request placed on the CPU bus (hereinafter referred to as "snoop storage elements") through activating one snoop enable line 77-80 and at least one storage element 81 which is employed for temporarily storing a snoop write back replacement address for Pentium™ Snoop Write Back cycle.

A second stage 62 includes a pair of stage multiplexers 83 and 84. A first stage multiplexer 83 is coupled to the information storage elements 65-68 through corresponding address/data input lines 85-88. The information signal from one of the information storage elements 65-68 is output by the first stage multiplexer 83 through a selected A/D output line 89 according to a binary representation of a plurality of information select lines 90. The second stage further includes a second stage multiplexer 84 coupled to the snoop storage elements 73-76 through corresponding snoop address lines 91-94 acting as inputs and a plurality of snoop address request lines 95 which are coupled to the second stage multiplexer 84 as select lines. Thus, based on the snoop address request lines 95, one of the snoop address requests is output from the second multiplexer 84 through a selected snoop output line 96 to a third stage multiplexer 97.

A third stage 63 includes the third stage multiplexer 97 coupled to the selected A/D and snoop output lines 89 and 96, respectively. Thereafter, either the information being transmitted through the address/data output line 89 or the snoop address request being transmitted through selected snoop output line 96 is transferred upon selection of an AD/snoop select line 98 and output through a selected AD/snoop output line 99 from the third stage multiplexer 97.

A fourth stage 64 includes a fourth stage multiplexer 100 coupled to the selected AD/snoop output line 99 from the third stage 63 and a snoop writeback line 101 transmitting an output from the snoop writeback storage element 81. The 36-bit information packet output from the holding element 60 is selected by a holding element select line 102 to be either the snoop writeback replacement address through selection of the snoop writeback line 101 or information or snoop address request through selection of the AD/snoop output line 99 and output to the output signal bits (labeled "HE[35:0]") of which the four most significant bits are input into the fifth multiplexer 45e as shown in FIG. 3C. For the first, second and fifth gates, these four most significant bits result in values for BEN[3:0] as shown in Tables 1-5 of Appendix A.

Referring to FIG. 6, the formatting controller 110 includes a plurality of state machines for controlling the holding element 60; namely, a data, address, snoop and trace state machines 111-114, respectively. These plurality of state machines receive certain internal command signals (at least VD, VA, VB, ABORT and LEADS) and active various select signals depending on these internal command signals. Both the data and address state machines 111-112 output those enable signals transmitted through the enable lines 69-72 associated with each of the four information storage elements 65-68 and the plurality of information select lines 90 for selecting one of the information storage elements for transmitting information through the first stage multiplexer 83. The configuration elements select the outputs from the data or address state machines 111 and 112 as input and control of the holding element 60.

The snoop state machine 113 controls the selection of signals through the stages of the holding element 60. More particularly, the snoop state machine 113 selects the appropriate snoop storage element for storing a snoop address request, which snoop address request being output of the second stage multiplexer 84 into the third stage multiplexer 97. Additionally, the snoop state machine 113 generates a select signal along the AD/snoop select line 98 for selecting whether the output of the third stage multiplexer 97 is an (i) address or data, or (ii) snoop address request whether the output of the fourth stage multiplexer 100 is the output of the third stage multiplexer 97 or the snoop write back line 101.

The formatting controller 110 further includes a trace state machine for generating trace output signals TVD, TVA, TVB, PIPE and SNOOP corresponding to the certain internal command signals; namely, VD, VA, VB, ABORT and LEADS. These trace output signals are used by ICE™ software to determine if there exists valid information on the CPU bus. These trace output signals are defined as follows:

(1) Trace Valid Data ("TVD")--indicates that there is valid data on the CPU bus for this frame.

(2) Trace Valid Address ("TVA")--indicates that there exists a valid address on the CPU bus for this frame.

(3) Trace Valid Burst ("TVB")--indicates that this bus cycle is a portion of a burst cycle so that the CPU bus contains four valid data packets.

(4) SNOOP--indicate that there is a valid snoop address on the CPU bus.

(5) PIPE--is a signal used only in "Raw" mode indicating that there exists two pending bus cycles.

The difference between the internal command signals and the trace output signals is that the trace output signals are mode dependent and configured accordingly. For example, as shown in a timing diagram of FIG. 7, the CPU is undergoing a single data transfer for each completed bus cycle as shown by the address strobe signal ("ADS#") and the bus ready signal ("BRDY#"). For the format mode, the TVA and TVB trace output signals are re-formatted in an aligned, synchronized manner. In Raw mode, however, the TVA and TVD signals are input into the ICE™ base unit as received so that the ICE™ base unit normally must track which TVA is associated with which TVD. As shown, in the present invention, the ICE™ base unit is not required to track the TVAs and TVDs because this is accomplished through the PIPE trace output signal, which is asserted when an TVA is asserted and de-asserted when the TVD associated with the TVA is asserted and de-asserted. In the event that the trace output signals are not used in favor of tracing all the Pentium™ CPU signals, it is extremely difficult for software to ascertain at any given moment in the trace if one or more bus cycles are pending, unless: (1) the trace is started after the Pentium™ CPU has completed all outstanding bus cycles and is stopped when filled with subsequent Pentium™ CPU bus cycles; or (2) the trace is stopped after all outstanding bus cycles are completed.

With the trace output signals being stored in the trace, the trace may be started and halted at any time and software can search through the trace with full cognizance what address goes with what data. In the "Format" mode, TVD, TVA, TVB and SNOOP are valid trace output signals providing much information to the ICE™ base unit. For example, if TVA and TVB are being simultaneously asserted, the current cycle is a burst cycle so that four valid data packets are to be placed on the CPU bus. Similarly, if TVA is asserted and TVB is de-asserted, the current cycle is a normal cycle transferring one data packet. In these cases, SNOOP indicates the address is the last snoop request done on the CPU bus.

In "Raw" mode, the PIPE trace output is used to determine if software needs to search back through the trace to the last address when TVD is asserted (when PIPE="0") or search back two addresses through the trace (when PIPE="1"). This allows software to correlate the correct address with its' associated data during when pending bus cycles are outstanding. It is contemplated, however, that multiple PIPE trace outputs could be used for CPU supporting more than two outstanding bus cycles.

Referring back to FIGS. 3A-3C, the holding element 60 receives 36-bits of information from first and second pipe components 43a and 43b and the formatting controller 110 receives the internal command signals from either the second input port 36 or the bus tracking component 31. After the above-discussed operations, the holding element 60 transfers a 32-bit information packet to the ICE™ interface circuit 47 to re-format and synchronously aligning address and data within the packet provided in "Format" mode before transferring the packet to the ICE™ base unit.

Referring to FIG. 8, the ICE™ interface circuit 47 includes a plurality of combinatorial logic circuits 121-126 having at least two inputs and a single output transferred to the ICE™ base unit as listed in Tables 1-5 of Appendix A. When in "Format" mode these combinatorial logic circuits 121-126 coordinate that the information is synchronously aligned and transferred to the ICE™ base unit for its maximum efficiency. With respect to a first combinatorial logic circuit 121, it receives as input eight most significant bits of the information packet from the holding element 60 (labeled "HE[31:24]") and the trace output signals from the trace state machine 114 of the formatting controller 110. The signals are input into a multiplexer 127. Except for the fifth gate array, the configuration elements of the gate array are programmed to select the HE[31:24] to be TOUT[31:24] to the ICE™ base unit, which are output from the multiplexer 127 and input into a mask element 128 (e.g., AND gate with an enable signal) transferring a null byte (all logic "0" signals) in lieu of HE[31:24] if the mask element 128 is enabled. In the preferred embodiment, the mask element 128 is enabled (logic "1") unless the gate array is the third gate array and is operating in a burst cycle.

With respect to a second combinatorial circuit 122, next eight most significant bits from both the holding element 60 "HE[23:16]" and the pipe component 43a "PIPE[23:16]" are input into a multiplexer 130. The second combinatorial circuit 122 usually outputs HE[23:16] as output signals TOUT[23:16] to the ICE™ base unit, except if the second combinatorial circuit is within the fifth gate array. This allow signals asynchronous to ADS# to be sent to the ICE™ base unit under software control.

With respect to a third combinatorial circuit 123, it outputs the next three most significant bits of the packet (i.e., TOUT[15:13]) to the ICE™ base unit. The contents of TOUT[15:13] is normally corresponding signals HE[15:13] from the holding element, except when the gate array is the fifth gate array in which TOUT[15:13] is equivalent to IC[2:0] as defined in Appendix B.

With reference to a fourth combinatorial circuit 124, it simply passes HE[12:5] with appropriate delays through as output signals TOUT[12:5]. The delays are incurred so that TOUT[12:5] will be input into the ICE™ base unit concurrently with the other output signals.

With respect to a fifth combinatorial circuit 125, it outputs TOUT[4:3] which includes the fourth and fifth bits of the address A[4:3] for the third gate array. The fifth combinatorial circuit 125 includes HE[4:3] being latched and input into a pair of exclusive-or gates ("XORs") 132 and 133 and a count address "CA[1:0]", generated by the formatting component, being input into the pair of XORs 132 and 133. The formatting component generates the count address bits CA[1] and CA[0] to have different binary values if the CPU is in a burst cycle. This is done to increment A[4:3] during the burst cycle to avoid problems if a burst cycle is requested during a normal data transfer. (See Table F below). For a normal bus cycle, however, the formatting component sets CA[1] and CA[0] equal so that the output TOUT[4:3] is not incremented.

With reference to the sixth combinatorial logic component 126, HE[2:0] is latched and input into a mask element 135 which is enabled by the formatting component activating a low address enable ("LAE"). In the third gate array, when a burst cycle occurs, all 64 bits are Valid on the data bus. The byte enables, which are used to generate A[2:0] and AH[2:0] are not always valid. Therefore, during a burst cycle, A[2:0] is always inactive (logic "0") and AH[2:0] is always active (logic "1"). The second portion to the transmission transmits A[2:0] to the pipe component 43a which, in turn, transfers A[2:0] to the holding element 60. The holding element 60 transfers A[2:0] into HE[2:0] of the trace.

Referring back to FIGS. 3A-3C, the filtering circuitry 33a and 33b enables a testing operator to selectively trace a desired type of bus cycle (e.g., memory read cycle, input/output write cycle, etc.). Due to the pipelined nature of the gate arrays, the filtering circuitry is operational only in the fifth gate array. Conventionally, any filtering of bus types is accomplished by the word recognizers in the ICE™ base unit which uses very limited vital resources.

The filtering circuitry comprises a bus cycle filter 33a and a force filter 33b. As shown in FIG. 9, the bus cycle filter 33a comprises a programmable logic array ("PLA") 140 receiving as input signals the internal command signals (VB, VA, VB, ABORT, LEADS) from the bus tracking component of the fifth gate array, the byte-enables BE[7:0]# from the third gate array through the second input port and various control signals including M/IO#, D/C#, ADS#, BOFF#, CACHE#, W/R#, EADS# BRDY#, CRDY#, KEN#, NA#, HLDA and HITM#. Collectively, these signals are representative of all the CPU bus cycle types.

The PLA 140 translates the above-identified signals into a unique 5-bit binary representation of a bus cycle type for use as selecting signal lines 141 for multiple-input multiplexer 142 receiving inputs from the configuration element 19 through a number of bus-type lines 143 corresponding in number to the number of bus cycle types. Each of the inputs correspond to a different CPU bus cycle type. The configuration element 19 output an active-high voltage signal onto a corresponding bus-type line 143 if its corresponding bus cycle type is selected and a low-voltage signal if not.

For example, suppose the operator desires only to trace memory read cycles. Upon detection of a memory read cycle, the PLA 140 outputs a binary number corresponding in number to placement of a bus type line designated to memory read cycles. Since memory read cycles are to be traced, the corresponding bus-type line 143 has an active signal thereon. Thus, when selected by the selecting signal lines 141, a filter line 144 is active. However, upon detection of another bus cycle type, its corresponding input line would be inactive so that the filter line 144 is inactive. The filter line 144 is latched by a latch element 145 for proper delay and an output filter line 146 is coupled to the force filter 33b which, in turn, generates a valid trace frame signal (VTF#) which indicates to the ICE™ base unit to trace or not trace the particular bus cycle.

Referring to FIG. 10, the force filter 33b is primarily used to filter non-bus type cycles such as breakpoints. This is accomplished by a plurality of logic gates 150a-150n ("n" being an arbitrary number) in parallel for outputting the non-bus type information from the Pipe component 43a via a non-bus filter lines 151a-151n (see FIGS. 3A-3C) when enabled by its corresponding mask enable 152a-152n. The mask enable lines 152a-152n are activated by the configuration element 19. The outputs of each of the logic gates 150a-150n are input into a first input of a corresponding plurality of XOR gates 153a-153n along with a value register 154a-154n from the configuration element 19, operating as a check of the output of the logic gates 150a-150n, is input into a second input of the corresponding XOR 153a-153n, respectively. Thus, according to a truth table of Table B illustrated below, the VTF# signal would be asserted indicating to the ICE™ base unit to trace the bus cycle based on the following:

                  TABLE B                                                          ______________________________________                                         Truth Table for Force Filter Component                                         Pipe Input                                                                               Mask          Value  VTF#                                            ______________________________________                                         X         0             1      1                                               X         0             0      0                                               0         1             1      1                                               1         1             1      0                                               0         1             0      0                                               1         1             0      1                                               ______________________________________                                    

Thus, for all cycles (bus and non-bus cycles), the force filter of the filtering circuitry is constructed according to Table C:

                  TABLE C                                                          ______________________________________                                         Truth Table for the Filtering Circuitry                                        Pipe Input Mask   Value       Filter                                                                              VTF#                                        ______________________________________                                         X          0      0           0    1                                           X          0      0           1    0                                           X          0      1           X    0                                           0          1      0           0    1                                           0          1      0           1    0                                           1          1      0           X    0                                           0          1      1           X    0                                           1          1      1           0    1                                           1          1      1           1    0                                           ______________________________________                                    

The address translation circuitry re-formats implicit addresses into explicit address. This is done to simplify programming of the word recognizers in the ICE™ base unit so as to simplify the software needed to set up the word recognizers for boundary ranges. The byte enables need to be explicit (correlate exactly to what operation is desired). As shown, an address generated directly from the Pentium™ CPU includes byte enables but does not have the three least significant address bits

Referring to FIG. 11, the first portion 34a of the address translation circuitry is illustrated and outputting valid information only within the third gate array. The purpose of the first portion 34a is to determine the high address boundary constraint "AH[2:0]" which signifies an upper boundary condition in order to give the highest byte address currently on the CPU bus for use by the word recognizers in the ICE™ to recognize byte addresses on a byte granularity instead of a packet granularity. The first portion includes a multiplexer 160 coupled to the latch component 42 to receive as input the byte-enables BE[7:0]# being input from the plurality of signal lines 41 as TIN[31:24] (see FIG. 2 and Table 3 of Appendix A). More specifically, BE[3:1]# and BE[7:5]# are input into the multiplexer 160 and either BE[3:1]# or BE[7:5]# is output from the multiplexer 160 through three output lines 161-163. The selection of BE[3:1]# or BE[7:5]# is accomplished through a select line 164 being an output of a NAND gate 165 having as inputs BE[7:4]#. If any of the BE[7:4]# are asserted (logic "0"), the NAND gate 165 outputs a logic "1" to a first high address boundary constraint bit AH[2] and selects the BE[7:5]# to be output from the multiplexer 160. Otherwise, the NAND gate 165 outputs a logic "0" to AH[2] and selects the BE[3:1]#.

In any event, a first and second byte enables transferred by a first and second output lines 161 and 162 are input into a second NAND gate 166 in which an output of the second NAND gate 166 represents a second high address boundary constraint bit "AH[1]." The first and a third byte enable transferred by the first and a third output lines 161 and 163 are input into a second multiplexer 167 being selected by the output of the second NAND gate 166. The output of the second multiplexer 167 is inverted and stored as a third high address boundary constraint bit "AH[0]." It is contemplated, however, that the first portion 34a of the address transition circuitry could be designed in a number of different constructions so as to at least comply with the truth table shown in Table D.

                  TABLE D                                                          ______________________________________                                         Truth Table for First Portion of the Address Translation Circuitry             BE[7:0]#                     AH[2:0]                                           7   6      5      4    3    2    1    0    2    1    0                         ______________________________________                                         0   X      X      X    X    X    X    X    1    1    1                         1   0      X      X    X    X    X    X    1    1    0                         1   1      0      X    X    X    X    X    1    0    1                         1   1      1      0    X    X    X    X    1    0    0                         1   1      1      1    0    X    X    X    0    1    1                         1   1      1      1    1    0    X    X    0    1    0                         1   1      1      1    1    1    0    X    0    0    1                         1   1      1      1    1    1    1    0    0    0    0                         ______________________________________                                    

Referring to FIG. 12, the second portion 34b of the address translation circuitry is illustrated. The purpose of the second portion 34b is to determine A[2:0] which signifies an lower boundary condition in order to give the lowest byte address currently on the data bus. The second portion 34b includes a multiplexer 170 also coupled to the latch component 42 to receive as input the byte-enables BE[7:0]# as shown in FIG. 2 and Table 3 of Appendix A. BE[2:0]# and BE[6:4]# are input into the multiplexer 170 and either BE[2:0]# or BE[6:4]# is output from the multiplexer 170 through three output lines 171-173. The selection of BE[2:0]# or BE[6:4]# is accomplished through a select line 174 being an output of a NAND gate 175 having as inputs BE[3:0]#. If any of the BE[3:0]# are asserted (logic "0"), the NAND gate 175 outputs a logic "1" which selects BE[2:0]# to be output from the multiplexer 170 and the logic "1" is inverted and stored as A[2]. Otherwise, the NAND gate 175 outputs a logic "0" so as to store a logic "1" in A[2] and selects BE[6:4]#.

In any event, a first and second byte enables BE[1:0]# or BE[5:4]# transferred by a first and second output lines 171 and 172 are input into a second NAND gate 176 in which an output of the second NAND gate 176 is inverted to represent A[1]. The first and a third byte enable are input into a second multiplexer 177 being selected by the output of the second NAND gate 176. The output of the second multiplexer 177 is stored as A[0]. It is contemplated, however, that the second portion 34b of the address transition circuitry could be designed in a number of different constructions so as to at least comply with the truth table shown in Table E.

                  TABLE E                                                          ______________________________________                                         Truth Table for a Second Portion of the Address Translation Circuitry          BE[7:0]#                     A[2:0]                                            7   6      5      4    3    2    1    0    2    1    0                         ______________________________________                                         0   X      X      X    X    X    X    X    1    1    1                         1   0      X      X    X    X    X    X    1    1    0                         1   1      0      X    X    X    X    X    1    0    1                         1   1      1      0    X    X    X    X    1    0    0                         1   1      1      1    0    X    X    X    0    1    1                         1   1      1      1    1    0    X    X    0    1    0                         1   1      1      1    1    1    0    X    0    0    1                         1   1      1      1    1    1    1    0    0    0    0                         ______________________________________                                    

As illustrated in FIGS. 11-12 and Tables D-E, the address translation circuitry calculates the value of A[2:0] which is associated to an address range set to the binary number representing the least significant byte enable that is asserted. For example, if only a fourth and fifth byte enables BE[4:3]# are enabled, A[2:0] would be equal to binary "011" representing BE[3]#. The address translation circuitry further calculates AH[2:0] being a 3-bit binary number set to the number value of the most significant byte enable that is asserted. Using the previous example, AH[2:0] would equal binary number "100".

As shown in FIGS. 3A-3C, the address translation circuitry further includes a third portion 34c operational only for the first and second gate arrays to overcome a debugging problem associated with the Pentium™ CPU. More particularly, the Pentium™ CPU may alter its current bus cycle from a non-burst read bus cycle to a burst read bus cycle. Thus, the byte-enables, all of which are usually asserted for a burst read cycle since external hardware may want to cache a 32-byte read, are commonly incorrect. As a result, if such an event occurs, a "Force Zero" signal line 48 from the formatting component 32 is asserted (logic "0") so that the byte enables are asserted i.e., BEN[3:0]="0" and a "Force One" signal line 49 from the formatting component 32 is asserted (logic "1") (See FIGS. 3A-3C). Otherwise, the Force Zero line 48 remains de-asserted so that AH[2:0] or BEN[3:0]# is set to "111" or "1111" respectively for the third gate array.

The address translation circuitry further includes a fourth portion within the ICE™ filtering circuitry to increment A[4:3] appropriately for burst cycles. This is accomplished through the fifth combinatorial logic circuit 125 as illustrated in FIG. 8 to function according to Table F when the count address bits CA[1] and CA[0] are set by the formatting controller to be opposite to one another.

                  TABLE F                                                          ______________________________________                                         Truth Table for A[4] and A[3] For a Pentium ™ Burst Cycle                             Address for                                                                               Address for                                                                            Address for                                                                              Address for                                       First      Second Data                                                                            Third Data                                                                               Fourth Data                                       Transfer   Transfer                                                                               Transfer  Transfer                                A4  A3    Cycle      Cycle   Cycle     Cycle                                   ______________________________________                                         0   0     00H        08H     10H       18H                                     0   1     08H        00H     18H       10H                                     1   0     10H        18H     00H       08H                                     1   1     18H        10H     08H       00H                                     ______________________________________                                    

The present invention described herein may be designed using many different circuit designs. While the present invention has been described in terms of a specific embodiment, other embodiments may come to mind to those skilled in the art without departure from the spirit and scope of the present invention. The invention should, therefore, be measured in terms of the claims which follow.

APPENDIX A

                  TABLE 1                                                          ______________________________________                                         Inputs into the first input port TIN[31:0] and outputs from the                first output port TOUT [31:0] and BEN[3:0] of the first Gate Array.            SIGNAL                SIGNAL                                                   NAME        INPUT     NAME        OUTPUT                                       ______________________________________                                         TIN0        D0        TOUT0       D0                                           TIN1        D1        TOUT1       D1                                           TIN2        D2        TOUT2       D2                                           TIN3        D3        TOUT3       D3                                           TIN4        D4        TOUT4       D4                                           TIN5        D5        TOUT5       D5                                           TIN6        D6        TOUT6       D6                                           TIN7        D7        TOUT7       D7                                           TIN8        D8        TOUT8       D8                                           TIN9        D9        TOUT9       D9                                           TIN10       D10       TOUT10      D10                                          TIN11       D11       TOUT11      D11                                          TIN12       D12       TOUT12      D12                                          TIN13       D13       TOUT13      D13                                          TIN14       D14       TOUT14      D14                                          TIN15       D15       TOUT15      D15                                          TIN16       D16       TOUT16      D16                                          TIN17       D17       TOUT17      D17                                          TIN18       D18       TOUT18      D18                                          TIN19       D19       TOUT19      D19                                          TIN20       D20       TOUT20      D20                                          TIN21       D21       TOUT21      D21                                          TIN22       D22       TOUT22      D22                                          TIN23       D23       TOUT23      D23                                          TIN24       D24       TOUT24      D24                                          TIN25       D25       TOUT25      D25                                          TIN26       D26       TOUT26      D26                                          TIN27       D27       TOUT27      D27                                          TIN28       D28       TOUT28      D28                                          TIN29       D29       TOUT29      D29                                          TIN30       D30       TOUT30      D30                                          TIN31       D31       TOUT31      D31                                                                BEN0        BE0#                                                               BEN1        BE1#                                                               BEN2        BE2#                                                               BEN3        BE3#                                         ______________________________________                                    

                  TABLE 2                                                          ______________________________________                                         Inputs into the first input port TIN[31:0] and outputs from the                first output port TOUT [31:0] and BEN[3:0] of the second Gate Array.           SIGNAL                SIGNAL                                                   NAME        INPUT     NAME        OUTPUT                                       ______________________________________                                         TIN0        D32       TOUT0       D32                                          TIN1        D33       TOUT1       D33                                          TIN2        D34       TOUT2       D34                                          TIN3        D35       TOUT3       D35                                          TIN4        D36       TOUT4       D36                                          TIN5        D37       TOUT5       D37                                          TIN6        D38       TOUT6       D38                                          TIN7        D39       TOUT7       D39                                          TIN8        D40       TOUT8       D40                                          TIN9        D41       TOUT9       D41                                          TIN10       D42       TOUT10      D42                                          TIN11       D43       TOUT11      D43                                          TIN12       D44       TOUT12      D44                                          TIN13       D45       TOUT13      D45                                          TIN14       D46       TOUT14      D46                                          TIN15       D47       TOUT15      D47                                          TIN16       D48       TOUT16      D48                                          TIN17       D49       TOUT17      D49                                          TIN18       D50       TOUT18      D50                                          TIN19       D51       TOUT19      D51                                          TIN20       D52       TOUT20      D52                                          TIN21       D53       TOUT21      D53                                          TIN22       D54       TOUT22      D54                                          TIN23       D55       TOUT23      D55                                          TIN24       D56       TOUT24      D56                                          TIN25       D57       TOUT25      D57                                          TIN26       D58       TOUT26      D58                                          TIN27       D59       TOUT27      D59                                          TIN28       D60       TOUT28      D60                                          TIN29       D61       TOUT29      D61                                          TIN30       D62       TOUT30      D62                                          TIN31       D63       TOUT31      D63                                                                BEN0        BE4#                                                               BEN1        BE5#                                                               BEN2        BE6#                                                               BEN3        BE7#                                         ______________________________________                                    

                  TABLE 3                                                          ______________________________________                                         Inputs into the first input port TIN[31:0] and outputs from the                first output port TOUT [31:0] and BEN[3:0] of the third Gate Array.            SIGNAL                SIGNAL                                                   NAME        INPUT     NAME        OUTPUT                                       ______________________________________                                         TIN0        --        TOUT0       A0                                           TIN1        --        TOUT1       A1                                           TIN2        --        TOUT2       A2                                           TIN3        A3        TOUT3       A3                                           TIN4        A4        TOUT4       A4                                           TIN5        A5        TOUT5       A5                                           TIN6        A6        TOUT6       A6                                           TIN7        A7        TOUT7       A7                                           TIN8        A8        TOUT8       A8                                           TIN9        A9        TOUT9       A9                                           TIN10       A10       TOUT10      A10                                          TIN11       A11       TOUT11      A11                                          TIN12       A12       TOUT12      A12                                          TIN13       A13       TOUT13      A13                                          TIN14       A14       TOUT14      A14                                          TIN15       A15       TOUT15      A15                                          TIN16       A16       TOUT16      A16                                          TIN17       A17       TOUT17      A17                                          TIN18       A18       TOUT18      A18                                          TIN19       A19       TOUT19      A19                                          TIN20       A20       TOUT20      A20                                          TIN21       A21       TOUT21      A21                                          TIN22       A22       TOUT22      A22                                          TIN23       A23       TOUT23      A23                                          TIN24       BE0#      TOUT24      BE0#                                         TIN25       BE1#      TOUT25      BE1#                                         TIN26       BE2#      TOUT26      BE2#                                         TIN27       BE3#      TOUT27      BE3#                                         TIN28       BE4#      TOUT28      BE4#                                         TIN29       BE5#      TOUT29      BE5#                                         TIN30       BE6#      TOUT30      BE6#                                         TIN31       BE7#      TOUT31      BE7#                                                               BEN0        AH0                                                                BEN1        AH1                                                                BEN2        AH2                                                                BEN3        --                                           ______________________________________                                    

                  TABLE 4                                                          ______________________________________                                         Inputs into the first input port TIN[31:0] and outputs from the                first output port TOUT [31:0] and BEN[3:0] of the fourth Gate Array.           SIGNAL                 SIGNAL                                                  NAME       INPUT       NAME       OUTPUT                                       ______________________________________                                         TIN0       A24         TOUT0      A24                                          TIN1       A25         TOUT1      A25                                          TIN2       A26         TOUT2      A26                                          TIN3       A27         TOUT3      A27                                          TIN4       A28         TOUT4      A28                                          TIN5       A29         TOUT5      A29                                          TIN6       A30         TOUT6      A30                                          TIN7       A31         TOUT7      A31                                          TIN8       --          TOUT8                                                   TIN9       --          TOUT9                                                   TIN10      --          TOUT10                                                  TIN11      --          TOUT11                                                  TIN12      A20M#       TOUT12     A20M#                                        TIN13      FLUSH#      TOUT13     FLUSH#                                       TIN14      INTR        TOUT14     INTR                                         TIN15      LOCK#       TOUT15     LOCK#                                        TIN16      SMI#        TOUT16     SMI#                                         TIN17      AMIACT#     TOUT17     SMIACT#                                      TIN18      PCD         TOUT18     PCD                                          TIN19      SCYC        TOUT19     SCYC                                         TIN20      NMI         TOUT20     NMI                                          TIN21      PWT         TOUT21     PWT                                          TIN22      AP          TOUT22     AP                                           TIN23      EWBE#       TOUT23     EWBE#                                        TIN24      BREQ        TOUT24     BREQ                                         TIN25      FERR#       TOUT25     FERR#                                        TIN26      FRCMC#      TOUT26     FRCMC#                                       TIN27      IERR#       TOUT27     IERR#                                        TIN28      IGNNE#      TOUT28     IGNNE#                                       TIN29      INV         TOUT29     INV                                          TIN30      HIT#        TOUT30     HIT#                                         TIN31      HOLD        TOUT31     HOLD                                                                BEN0       --                                                                  BEN1       --                                                                  BEN2       --                                                                  BEN3       --                                           ______________________________________                                    

                  TABLE 5                                                          ______________________________________                                         Inputs into the first input port TIN[31:0] and outputs from the                first output port TOUT [31:0] and BEN[3:0] of the fifth Gate Array.            SIGNAL                 SIGNAL                                                  NAME       INPUT       NAME       OUTPUT                                       ______________________________________                                         TIN0*      NA#         TOUT0      NA#                                          TIN1       CRDY#       TOUT1      CRDY#                                        TIN2*      ADS#        TOUT2      ADS#                                         TIN3*      BRDY#       TOUT3      BRDY#                                        TIN4*      KEN#        TOUT4      KEN#                                         TIN5*      CACHE#      TOUT5      CACHE#                                       TIN6*      HITM#       TOUT6      HITM#                                        TIN7*      HLDA        TOUT7      HLDA                                         TIN8*      BOFF#       TOUT8      BOFF#                                        TIN9*      AHOLD       TOUT9      AHOLD                                        TIN10*     D/C#        TOUT10     D/C#                                         TIN11*     W/R#        TOUT11     W/R#                                         TIN12*     M/IO#       TOUT12     M/IO#                                        TIN13      --          TOUT13     IC0                                          TIN14      --          TOUT14     IC1                                          TIN15      --          TOUT15     IC2                                          TIN16      INIT        TOUT16     INIT                                         TIN17*     RESET       TOUT17     RESET                                        TIN18*     IBT         TOUT18     IBT                                          TIN19*     IV          TOUT19     IV                                           TIN20*     IU          TOUT20     IU                                           TIN21*     EADS#       TOUT21     EADS#                                        TIN22      BP3         TOUT22     BP3                                          TIN23      BP2         TOUT23     BP2                                          TIN24      BP1         TOUT24     BP1                                          TIN25      BP0         TOUT25     BP0                                          TIN26      WB/WT#      TOUT26     WB/WT#                                       TIN27      --          TOUT27     PIPE                                         TIN28      --          TOUT28     TVB                                          TIN29      --          TOUT29     TVA                                          TIN30      --          TOUT30     TVD                                          TIN31      --          TOUT31     SNOOP                                                               BEN0       ICE MODE                                                            BEN1       RESET OUT                                                           BEN2       INIT OUT                                                            BEN3       VTF#                                         ______________________________________                                    

APPENDIX B

    ______________________________________                                         Symbol  Type*   Name and Function                                              ______________________________________                                         A20M#   I       When the address bit 20 mask pin is asserted, the                              Pentium ™ CPU emulates the address wraparound                               at one Mbyte which occurs on the 8086. When                                    A20M# is asserted, the Pentium ™ CPU masks                                  physical address bit 20 (A20) before performing a                              lookup to the internal caches or driving a memory                              cycle on the bus. The effect of A20M# is                                       undefined in protected mode. A20M# must be                                     asserted only when the CPU is in real mode.                    A31-A3  I/O     As outputs, the address lines of the CPU along                                 with the byte enables define the physical area of                              memory or I/O accessed. The external system                                    drives the inquire address to the CPU on                                       A31-A5.                                                        ADS#    O       The address status indicates that a new valid bus                              cycle is currently being driven by the Pentium ™                            CPU.                                                           AHOLD   I       In response to the assertion of address hold, the                              Pentium ™ CPU will stop driving the address                                 lines (A31-A3), and AP in the next clock. The                                  rest of the bus will remain active so data can be                              returned or driven for previously issued bus                                   cycles.                                                        AP      I/O     Address parity is driven by the Pentium ™ CPU                               with even parity information on all Pentium ™                               CPU generated cycles in the same clock that the                                address is driven. Even parity must be driven                                  back to the Pentium ™ CPU during inquire                                    cycles on this pin in the same clock as EADS# to                               ensure that the correct parity check status is                                 indicated by the Pentium ™ CPU.                             BE7#-BE0#                                                                              O       The byte enable pins are used to determine which                               bytes must be written to external memory, or                                   which bytes were requested by the CPU for the                                  current cycle. The byte enables are driven in                                  the same clock as the address lines (A31-3).                   BOFF#   I       The backoff input is used to abort all outstanding                             bus cycles that have not yet completed. In                                     response to BOFF#, the Pentium ™ CPU will                                   float all pins normally floated during bus hold in                             the next clock. The CPU remains in bus hold                                    until BOFF# is negated at which time the                                       Pentium ™ CPU restarts the aborted bus cycle(s)                             in their entirety.                                             BP[3:2] O       The breakpoint pins (BP3-0) externally indicate a              PM/BP[1:0]      breakpoint match when the debug registers                                      (DR3-0) are programmed to test for breakpoint                                  matches.                                                                       BP1 and BP0 are multiplexed with the                                           Performance Monitoring pins (PM1 and PM0).                                     The PB1 and PB0 bits in the Debug Mode                                         Control Register determine if the pins are                                     configured as breakpoint or performance                                        monitoring pins. The pins come out of reset                                    configured for performance monitoring.                         BRDY#   I       The burst ready input indicates that the external                              system has presented valid data on the data pins                               in response to a read or that the external system                              has accepted the Pentium ™ CPU data in                                      response to a write request.                                   BREQ    O       The bus request output indicates to the external                               system that the Pentium ™ CPU has internally                                generated a bus request. This signal is always                                 driven whether or not the Pentium ™ CPU is                                  driving its bus.                                               CACHE#  O       For Pentium ™ CPU-initiated cycles the cache                                pin indicates internal cacheability of the cycle                               (if a read), and indicates a burst writeback cycle                             (if a write). If this pin is driven inactive during                            a read cycle, Pentium ™ CPU will not cache                                  the returned data, regardless of the state of the                              KEN# pin. This pin is also used to determine                                   cycle length (number of transfers in the cycle).               CLK     I       The clock input provides the fundamental timing                                for the Pentium ™ CPU. Its frequency is the                                 internal operating frequency of the Pentium ™                               CPU and requires TTL levels.                                   D/C#    O       The Data/Code output is one of the primary bus                                 cycle definition pins. It is driven valid in the                               same clock as the ADS# signal is asserted. D/C#                                distinguishes between data and code or special                                 cycles.                                                        D63-D0  I/O     These are the 64 data lines for the CPU.                                       Lines D7-D0 define the least significant byte of                               the data bus; lines D63-D56 define the most                                    significant byte of the data bus. During reads, the                            CPU samples the data bus when BRDY# is                                         returned.                                                      EADS#   I       The signal indicates that a valid external address                             has been driven onto the Pentium ™ CPU                                      address pins to be used for an inquire cycle.                  EWBE#   I       The external write buffer empty input, when                                    active (high), indicates that a write cycle is                                 pending in the external system. When the                                       Pentium ™ CPU generates a write, and EWBE#                                  is sampled inactive, the Pentium ™ CPU will                                 hold off all subsequent writes to all Exclusive or                             Modified state lines in the data cache until all                               write cycles have completed, as indicated by                                   EWBE# being active.                                            FERR#   O       The floating point error pin is driven active when                             an unmasked floating point error occurs. FERR#                                 is similar to the ERROR# pin on the Intel 386 ™                             math coCPU. FERR# is included for                                              compatibility with systems using DOS type                                      floating point error reporting.                                FLUSH#  I       When asserted, the cache flush input forces the                                Pentium ™ CPU to writeback all modified lines                               in the data cache and invalidate its internal                                  caches. A Flush Acknowledge special cycle will                                 be generated by the Pentium ™ CPU indicating                                completion of the writeback and invalidation.                                  If FLUSH# is sampled low when RESET                                            transitions from high to low, tristate test                                    mode is entered.                                               FRCMC#  I       The Functional Redundancy Checking Master/                                     Checker mode input is used to determine whether                                the Pentium ™ CPU is configured in master                                   mode or checker mode. When configured as a                                     master, the Pentium ™ CPU drives its output                                 pins as required by the bus protocol. When                                     configured as a checker, the Pentium ™ CPU                                  tristates when outputs and samples the output                                  pins.                                                                          The configuration as a master/checker is set after                             RESET and may not be changed other than by a                                   subsequent RESET.                                              HIT#    O       The hit indication is driven to reflect the                                    outcome of an inquire cycle. If an inquire cycle                               hits a valid line in either the Pentium ™ CPU                               data or instruction cache, this pin is asserted                                two clocks after EADS# is sampled asserted.                                    If the inquire cycle misses Pentium ™ CPU                                   cache, this pin is negated two clocks after                                    EADS#. This pin changes its value only as a                                    result of an inquire cycle and retains its value                               between the cycles.                                            HITM#   O       The hit to a modified line output is driven to                                 reflect the outcome of an inquire cycle. It is                                 asserted after inquire cycles which resulted in a                              hit to a modified line in the data cache. It is used                           to inhibit another bus master from accessing the                               data until the line is completely written back.                HLDA    O       The bus hold acknowledge pin goes active in                                    response to a hold request driven to the CPU                                   on the HOLD pin. It indicates that the                                         Pentium ™ CPU has floated most of the                                       output pins and relinquished the bus to another                                local bus master. When leaving bus hold, HLDA                                  will be driven inactive and the Pentium ™ CPU                               will resume driving the bus. If the Pentium ™                               CPU has bus cycle pending, it will be driven in                                the same clock that HLDA is deasserted.                        HOLD    I       In response to the bus hold request, the                                       Pentium ™ CPU will float most of its                                        output and input/output pins and assert HLDA                                   after completing all outstanding bus cycles.                                   The Pentium ™ CPU will maintain its bus                                     in this state until HOLD is deasserted. HOLD is                                not recognized during LOCK cycles. The                                         Pentium ™ CPU will recognize HOLD during                                    reset.                                                         IBT     O       The instruction branch taken pin is driven active                              (high) for one clock to indicate that a branch                                 was taken. This output is always driven by the                                 Pentium ™ CPU.                                              IERR#   O       The internal error pin is used to indicate two                                 types of errors, internal parity errors and                                    functional redundancy errors. If a parity error                                occurs on a read from an internal array, the                                   Pentium ™ CPU will assert the IERR# pin                                     for one clock and then shutdown. If the                                        Pentium ™ CPU is configured as a checker                                    and a mismatch occurs between the value                                        sampled on the pins and the corresponding value                                computed internally, the Pentium ™ CPU will                                 assert IERR# two clocks after the mismatched                                   value is returned.                                             IGNNE#  I       This is the ignore numeric error input. This pin                               has no effect when the NE bit in CR0 is set to 1.                              When the CR0.NE bit is 0, and the IGNNE# pin                                   is asserted, the Pentium ™ CPU will ignore                                  any pending unmasked numeric exception and                                     continue executing floating point instructions                                 for the entire duration that this pin is asserted.                             When the CR0.NE bit is 0, IGNNE# is not                                        asserted, a pending unmasked numeric exception                                 exists (SW.ES = 1), and the floating point                                     instruction is one of FINIT, FCLEX, FSTENV,                                    FSAVE, FSTSW, FSTCW, FENI, FDISI, or                                           FSETPM, the Pentium ™ CPU will execute                                      the instruction in spite of the pending exception.                             When the CR0.NE bit is 0, IGNEE# is not                                        asserted, a pending unmasked numeric exception                                 exists (SW.ES = 1), and the floating point                                     instruction is one other than FINIT, FCLEX,                                    FSTENV, FSAVE, FSTSW, FSTCW, FENI,                                             FDISI, or FSETPM, the Pentium ™ CPU                                         will stop execution and wait for an external                                   interrupt.                                                     INIT    I       The Pentium ™ CPU initialization input pin                                  forces the Pentium ™ CPU to begin                                           execution in a known state. The CPU state                                      after INIT is the same as the state after RESET                                except that the internal caches, write buggers,                                and floating pint registers retain the values                                  they had prior to INIT. INIT may NOT be used in                                lieu of RESET after power-up.                                                  It INIT is sampled high when RESET transitions                                 from high to low, the Pentium ™ CPU will                                    perform built-in self test prior to the start                                  of program execution.                                          INTR    I       An active maskable interrupt input indicates that                              an external interrupt has been generated.                                      INTR must remain active until the first interrupt                              acknowledge cycle is generated to assure that the                              interrupt is recognized.                                       INV     I       The invalidation input determines the final cache                              line state (S or I) in case of an inquire cycle hit.                           It is sampled together with the address for the                                inquire cycle in the clock EADS# is sampled                                    active.                                                        IU      O       The u-pipe instruction complete output is                                      driven active (high) for 1 clock to indicate that                              an instruction in the u-pipeline has completed                                 execution. This pin is always driven by the                                    Pentium ™ CPU.                                              IV      O       The v-pipe instruction complete output is                                      driven active (high) for one clock to indicate that                            an instruction in the v-pipeline has completed                                 execution. This pin is always driven by the                                    Pentium ™ CPU.                                              KEN#    I       The cache enable pin is used to determine                                      whether the current cycle is cacheable or not and                              is consequently used to determine cycle length.                                When the Pentium ™ CPU generates a cycle                                    that can be cached (CACHE# asserted) and                                       KEN# is active, the cycle will be transformed                                  into a burst line fill cycle.                                  LOCK#   O       The bus lock pin indicates that the current                                    bus cycle is locked. The Pentium ™ CPU                                      will not allow a bus hold when LOCK# is                                        asserted (but AHOLD and BOFF# are allowed).                                    LOCK# goes active in the first clock of the first                              locked bus cycle and goes inactive after the                                   BRDY# is returned to the last locked bus                                       cycle. LOCK# is guaranteed to be deasserted                                    for at least one clock between back to back                                    locked cycles.                                                 M/IO#   O       The Memory/Input-Output is one of the primary                                  bus cycle definition pins. It is driven valid                                  in the same clock as the ADS# signal is asserted.                              M/IO# distinguishes between memory and I/O                                     cycles.                                                        NA#     I       An active next address input indicates that                                    the external memory system is ready to accept                                  a new bus cycle although all data transfers for                                the current cycle have not yet completed. The                                  Pentium ™ CPU will drive out a pending                                      cycle two clocks after NA# is asserted.                                        The Pentium ™ CPU supports up to 2                                          outstanding bus cycles.                                        NMI     I       The non-maskable interrupt request signal                                      indicates that an external non-maskable interrupt                              has been generated.                                            PCD     O       The page cache disable pin reflects the state                                  of the PCD bit in CR3, the Page Directory Entry,                               or the Page Table Entry. The purpose of PCD is                                 to provide an external cacheability indication                                 on a page by page basis.                                       PWT     O       The page write through pin reflects the state                                  of the PWT bit in CR3, the Page Directory Entry,                               or the Page Table Entry. The PWT pin is used                                   to provide an external writeback indication on a                               page by page basis.                                            RESET   I       Reset forces the Pentium ™ CPU to begin                                     execution at a known state. All the Pentium ™                               CPU internal caches will be invalidated upon the                               RESET. Modified lines in the data cache are not                                written back.                                                                  FLUSH#, FRCMC# and INIT are sampled when                                       RESET transitions from high to low to determine                                if tristate test mode or checker mode will be                                  entered, or if BIST will be run.                               SCYC    O       The split cycle output is asserted during                                      misaligned LOCKed transfers to indicate that                                   more than two cycles will be locked together.                                  This signal is defined for clocked cycles only. It                             is undefined for cycles which are not locked.                  SMI#    I       The System Management Interrupt causes a                                       system management interrupt request to be                                      latched internally. When the latched SMI# is                                   recognized on an instruction boundary, the CPU                                 enters System Management Mode.                                 SMIAT#  O       An active system management interrupt active                                   output indicates that the CPU is operating in                                  System Management Mode (SMM).                                  W/R#    O       Write/Read is one of the primary bus cycle                                     definition pins. It is driven valid in the same                                clock as the ADS# signal is asserted. W/R#                                     distinguishes between write and read cycles.                   WB/WT#  I       The writeback/writethrough input allows a data                                 cache line to be defined as write back or write                                through on a line by line basis. As a result,                                  it determines whether a cache line is initially in                             the S or E state in the data cache.                            ______________________________________                                     

What is claimed is:
 1. A circuit for testing an electronic component by transferring information placed on a bus by the electronic component to an ICE™ base unit, the circuit comprising:a bus tracking component coupled to at least the bus, said bus tracking component monitoring a first plurality of information signals propagating through the bus and generating a second plurality of information signals; a multiplexer coupled to said bus and said bus tracking component, said multiplexer receiving said second plurality of information signals and a third plurality of information signals; and a formatting component coupled to at least said multiplexer, said formatting component retaining the information including one of said second and third plurality of information signals output by said multiplexer until a particular bus cycle associated with the information has completed, re-formatting and transferring at least the information into the ICE™ base unit.
 2. The circuit according to claim 1, wherein said bus tracking component includes a plurality of state machines including a first state machine that signals said formatting component that a snoop cycle has occurred on the bus.
 3. The circuit according to claim 2, wherein said bus tracking component includes a second and third state machine operating in the alternative to monitor said first plurality of information signals transmitted onto said bus.
 4. The circuit according to claim 1, wherein said formatting component includes a holding element and a formatting controller.
 5. The circuit according to claim 1, wherein said holding element temporarily contains said information until signaled by said formatting controller to transfer said information.
 6. The circuit according to claim 1 further comprises a filtering circuitry coupled at least to said bus tracking component, said filtering circuitry asserting a valid trace frame signal upon detecting that a current cycle is permitted to be traced by said ICE™ base unit, said asserted valid trace frame signal informs said ICE™ base unit to trace a frame associated with said current cycle.
 7. The circuit according to claim 6, wherein said filtering circuitry includes a bus type filter that activates a first signal line upon detection that said current cycle is a bus cycle permitted to be traced by said ICE™ base unit, and a force filter that activates a second signal line upon detecting that said current cycle is a non-bus cycle permitted to be traced by said ICE™ base unit, said valid trace frame signal is activated if at least one of said first and second signal lines is activated.
 8. The circuit according to claim 1 further comprises an address translation circuitry to calculate address information required by the ICE™ base unit, said address translation circuitry includesa first translator which calculates an upper boundary condition in order to obtain a highest byte address currently on the bus for use by said ICE™ base unit; and second translator which calculates a lower boundary condition in order to obtain a lowest byte address currently on the bus for use by said ICE™ base unit.
 9. A circuit for testing an electronic component by transferring information placed onto a bus by the electronic component to an ICE™ base unit, the circuit comprising:a first translator which calculates an upper boundary condition in order to obtain a highest byte address currently on the bus for use by said ICE™ base unit; second translator which calculates a lower boundary condition in order to obtain a lowest byte address currently on the bus for use by said ICE™ base unit; a bus tracking component coupled to the bus; and filtering circuitry coupled at least to said bus tracking component, said filtering circuitry asserts a valid trace frame signal upon detecting that a current cycle is a cycle permitted to be traced by said ICE™ base unit, said asserted valid trace frame signal informs said ICE™ base unit to trace a frame associated with said current cycle.
 10. The circuit according to claim 9 wherein said bus tracking component monitoring a first plurality of information signals propagating through the bus and generating a second plurality of information signals.
 11. The circuit according to claim 10 further comprising:a multiplexer coupled to said bus and said bus tracking component, said multiplexer receiving said second plurality of information signals and a third plurality of information signals, said multiplexer outputting one of said second and third plurality of information signals into a formatting component; and said formatting component coupled to at least said multiplexer, said formatting component retaining the information until a particular bus cycle associated with the information has completed, re-formatting at least the information and transferring at least the information into the ICE™ base unit. 